U.S. patent number 4,001,513 [Application Number 05/600,649] was granted by the patent office on 1977-01-04 for method and apparatus for the detection of fraudulent toll telephone calls.
This patent grant is currently assigned to Northern Electric Company Limited. Invention is credited to David Charles Naylor.
United States Patent |
4,001,513 |
Naylor |
January 4, 1977 |
Method and apparatus for the detection of fraudulent toll telephone
calls
Abstract
Fraudulent toll telephone calls are detected by the recognition
of extraneous supervisory signals which are generated in the
originating office in response to a perpetrator placing such a
call. The invention provides a means of detecting a second
proceed-to-send signal received at the originating office and of
recording in memory means the identities of the calling and called
parties. Timing means for achieving the detection is connected to
the automatic message accounting trunk circuit of the originating
office and, upon detection, an MF receiver is also connected
thereto for a predetermined interval of time.
Inventors: |
Naylor; David Charles
(Georgetown, CA) |
Assignee: |
Northern Electric Company
Limited (Montreal, CA)
|
Family
ID: |
24404495 |
Appl.
No.: |
05/600,649 |
Filed: |
July 31, 1975 |
Current U.S.
Class: |
379/115.01;
379/235; 379/189; 379/245 |
Current CPC
Class: |
H04M
15/04 (20130101) |
Current International
Class: |
H04M
15/04 (20060101); H04M 015/12 () |
Field of
Search: |
;179/7,7.1R,18DA,84VF,84R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Brigance; Gerald L.
Attorney, Agent or Firm: Turpin; Frank
Claims
What is claimed is:
1. In a telephone system comprising an originating office, and a
destination office connected to said originating office via a
transmission path, said originating office comprising a toll call
processing system and an automatic message accounting system
including at least one automatic message accounting trunk circuit
connected to said call processing system, and wherein control
signalling between said offices comprises using the predetermined
presence or absence of a single frequency signal on said
transmission path including a proceed-to-send signal transmitted
from said destination office to said originating office, a method
of detecting a fraudulent toll telephone call comprising the step
of detecting a supervisory signal at the automatic message
accounting trunk circuit, said supervisory signal corresponding to
a second proceed-to-send signal from the destination office.
2. A method as defined in claim 1 comprising the further step of
causing a coded entry associated with the call in progress to be
entered into the billing information memory means of the automatic
message accounting system in response to said detection.
3. A method as defined in claim 1, comprising the further step of
connecting a multifrequency receiver to said automatic message
accounting trunk circuit in response to said detection.
4. A method as defined in claim 3, comprising the additional step
of transferring the dialling information received by the
multifrequency receiver to the billing information memory means of
the automatic message accounting system.
5. A method as defined in claim 4 comprising the further step of
providing the billing information memory means of the automatic
message accounting system with a flag signal associated with the
call in progress in response to said detection.
6. In a telephone system comprising an originating office, a
destination office connected to said originating station via a
transmission path and wherein control signalling between said
offices comprises using the predetermined presence or absence of a
single frequency signal on said transmission path including a
proceed-to-send signal transmitted from said destination office to
said originating office, a method of detecting a fraudulent toll
call comprising the step of detecting the presence of a second
proceed-to-send signal at said originating office during any one
call.
7. A telephone system comprising in combination, an originating
office and a destination office connectable together via a
transmission path, the originating office comprising a toll call
processing system including an outgoing single frequency circuit
and an automatic message accounting system including an automatic
message accounting trunk circuit, the destination office comprising
an incoming single frequency signalling circuit, wherein control
signalling between said originating and destination offices is
achieved using the predetermined presence or absence of a single
frequency signal on said transmission path including a
proceed-to-send signal transmitted from said destination office to
said originating office, and means for detecting the presence of a
second proceed-to-send signal appearing at said originating station
during any one call.
8. A telephone system as defined in claim 7 and further comprising
means responsive to a signal from said detection means for causing
a coded entry associated with the call in progress to be entered
into the billing information memory means of the automatic message
accounting system.
9. A telephone system as defined in claim 7 wherein said detection
means comprises means for acknowledging the presence of said second
proceed-to-send signal at said automatic message accounting trunk
circuit.
10. A telephone system as defined in claim 7 further comprising, a
multifrequency receiver circuit and means for connecting said
receiver circuit to said automatic message accounting trunk circuit
in response to said acknowledgement of the presence of said second
proceed-to-send signal.
11. A telephone system as defined in claim 9, further comprising,
means for generating and storing a flag signal associated with the
call in progress in the billing information memory means of said
automatic message accounting system in response to said
acknowledgement of the presence of said second proceed-to-send
signal.
Description
This application relates generally to telephone system and more
particularly to the method and apparatus for the detection of
fraudulent toll telephone calls.
It is generally recognized that a sizeable proportion of toll calls
are fraudulent in nature. That is, these calls are placed in such a
way that the automatic message accounting system of an originating
toll office is induced into charging erroneously for the calls.
The most common method of placing fraudulent toll calls has been to
use a so-called "blue box". This piece of apparatus which is
coupled to the subscriber telephone set normally consists of an
oscillator adapted to provide an output signal which simulates
exactly the in-band single frequency control signal of the
North-American toll telephone network, and a multifrequency (MF)
generator including a set of pushbutton keys to simulate the MF
signalling also used in the toll telephone network.
In order to use his blue box, the user accesses the direct distance
dialling (DDD) network by placing a toll call to a called party in
a near destination office and at the first ringing signals to the
called party, the call is cancelled at the destination toll office
by requesting service as for a new call, by using the blue box.
This causes the equipment in the destination toll office to accede
to the request by dropping the call in progress and by sending a
second proceed-to-send signal to the originating office. The blue
box user then keys a new called number to which the destination
office reacts by routing the call to the called party. However all
of the signalling which takes place from the cancellation of the
first call to the routing of the call to the second called party
appears on the speech path of the originating office. Therefore,
the automatic message accounting system at the originating office
is not aware of any changes in the original call and the blue box
user only gets billed for a call to the near toll office which he
originally accessed.
There have been numerous attempts at preventing and/or detecting
the use of these blue boxes. The most common method of detecting
the use of a blue box is the detection of a foreign single
frequency control signal generated by the blue box and which
appears at the trunk circuit of the automatic message accounting
system. If a blue box is used, this foreign control signal will
indeed appear on the speech path of the trunk circuit. However,
because the control signal is an inband signal, it must be
differentiated from voice signals; otherwise speech signals will
trigger the detection circuitry. This requires the use of very
sophisticated, and therefore expensive, frequency separation and
detection circuitry.
I have found that the detection of a blue box user may be made very
simply, reliably and economically. Whenever a blue box user
operates his device to cancel his first-dialled call, the equipment
at the destination office responds by reconnecting a
receiver/sender to the transmission path. The receiver/sender
signals the originating office to send the called number by sending
a second proceed-to-send signal on the transmission line.
This signal is detected and converted to a direct current
supervisory signal by the outgoing single frequency unit of the
originating office and fed back to the automatic message accounting
trunk circuit because the system is expecting an off-hook control
signal from the destination office. Since this supervisory signal
is a direct current supervisory signal of a predetermined duration,
it may be recognized with relative ease. Therefore, I have found
that a fraudulent user of the toll system may be detected by
detecting the presence of a second proceed-to-send signal at the
originating office during any one toll call.
Following detection, the operating company has the option of
causing the automatic message accounting system to record the
ensuing fraudulent called number and thereby billing the calling
party for his fraudulent call, and/or denying the calling party the
use of the toll system by cancelling the call. In any case, the
identity of the calling number may be identified by flagging the
records of the message accounting system.
An example embodiment of the invention will now be described in
conjunction with the drawings in which:
FIG. 1 is a block circuit diagram of a system in accordance with
the invention;
FIG. 2 is a waveform diagram illustrating control signals at
various points in the system of FIG. 1; and
FIGS. 3 and 4 are sequence flow charts illustrating the operation
of the system of FIG. 1 with and without the invention
respectively.
FIG. 1 is a block circuit diagram showing a portion of the
telephone network. Only those parts of the system necessary to
explain the invention are shown and all of the blocks within the
system are well known to persons knowledgeable in the telephone
art.
FIG. 1 shows an originating toll telephone office 100 connected to
a local telephone office 10, and a destination toll telephone
office 20. The local office 10 is shown to comprise a switching
network 11 and a trunk circuit 12 for connection of the local
office 10 to the toll office 100. The local office 10 is also
connected to a subscriber telephone set 9 which in turn is
connected to a fraud box 8 (blue box).
The circuitry of the fraud box is presently well known in some
circles since thousands of units are in use. It consists of an
audio oscillator capable of providing an output signal which
simulates exactly the in-band single frequency control signal used
between toll offices of the North-American telephone network and a
multifrequency (MF) generator including a set of pushbutton keys
for emulating the MF signalling also used in the toll telephone
network.
The toll office 100 is shown to comprise an automatic message
accounting (AMA) trunk 101 for connection to the local office 10
and to an outgoing trunk 102 via a switching network 103. The
outgoing trunk 102 is connected to an outgoing single frequency
unit 104 and connectable to an MF sender 105 which is connected to
a common controlling means 106 through a switch 107. The
controlling means 106 controls the entire functioning of the office
and transfers the information necessary for the billing of a toll
call from the AMA trunk circuit 101 to billing equipment 108 which
stores the billing information for subsequent processing in a
memory means such as tape 109.
For purposes of describing the invention, an AMA trunk circuit is
defined as that piece of apparatus which is responsive to
supervisory signals necessary to the billing of a toll call. The
configuration shown in toll office 100 is that which is
conventional and common the the Electronic Switching Systems (ESS)
of the Western Electric Company and the Stored Program Switching
System of the Northern Electric Company (SP-1) when they are
equipped with an automatic message accounting system (AMA). All of
the above systems have been the object of numerous patents and have
been extensively documented in the literature. Generally, a toll
office such as block 100 serves as the gateway to the toll
telephone network. It is accessed from a local office such as block
10 and accesses another toll office such as block 20. The
supervisory information for controlling and billing the call to the
calling subscriber appears at a trunk circuit such as the AMA trunk
101 and is made available for processing by the common controlling
means 106 via a scanner circuit therein (not shown) which
periodically samples the information appearing at the trunk 101.
Through the use of well-known software techniques, the common
controlling means 106 is able to determine the characteristics and
the identity of the signals it receives from the trunk circuit
101.
The toll office 100 is shown to also have an MF receiver 110
connectable to the AMA trunk circuit 101 by a switch 111 controlled
by the common controlling means 106. This receiver circuit may be a
conventional multifrequency receiver such as are used extensively
in telephone offices. Its function is to receive multifrequency
signals and convert them to direct current voltage level signals.
Its purpose in this system will be explained below.
The toll office 20 is shown to comprise an incoming trunk 21
connected to an incoming single frequency unit 22, to a switching
network 23 and to an MF register/sender 24. The office 20 may be
connected to other parts of the telephone network via a plurality
of transmission paths 1, 2 . . . N and is connected to the toll
office 100 via a transmission path having channels A and B -- one
for each direction of transmission.
OPERATION OF THE SYSTEM
A clearer understanding of the operation of the system as it
relates to the invention may be gained by reference to FIG. 2 of
the drawings which is a waveform diagram of supervisory and control
signals at various points in the system and to FIGS. 3 and 4 which
are sequence flow charts illustrating the operational differences
between a prior art system and the invention.
The subscriber initiates a long distance or toll call in the
conventional manner, that is, by going off-hook and dialling the
digit 1. This action causes the local office 10 to connect the
subscriber's line through the network 11 and the trunk circuit 12
to the toll office 100. As the called number is dialled, the digits
are recorded by the billing equipment 108-109 of the automatic
message accounting system which also records the identity of the
calling party. The called number is passed along to the
multifrequency (MF) sender 105 attached to an outgoing trunk 102
which is connected to a destination toll office 20 via a
transmission path having channels A and B, one for each direction
of transmission, as is conventional in the toll telephone
network.
The outgoing trunk 102 causes the outgoing single frequency (SF)
unit 104 to remove the 2600 hertz control signal from channel A.
The removal of this control signal informs the incoming single
frequency (SF) unit 22 of the toll office 20 that a call is in
progress and that service is requested. The incoming SF unit then
causes the incoming trunk 21 to attach the register/sender 24
thereto. When the register/sender 24 is ready to receive the digits
of the called number, it signals the incoming SF unit 22 which
responds by momentarily removing the 2600 hertz control signal from
channel B of the transmission path to the office 100. This is a
proceed-to-send signal to the originating office. The duration of
this break in signal is nominally 200 milliseconds. When it is
removed for more than two seconds, the originating office
interprets the removal as an indication that the called party has
gone off-hook, e.g. that the called party has answered, and when it
is removed for less than 75 milliseconds, it is interpreted as
noise (hit on the line) and ignored.
The proceed-to-send signal is detected by the outgoing SF unit 104
which changes its direct current (DC) supervisory signal to the
outgoing trunk 102. Because the MF sender 105 is still connected
thereto, the outgoing trunk 102 passes this change in the
supervisory DC signal to it instead of to the AMA trunk 101 which
is waiting for an off-hook indication in order to start timing the
call. The MF sender 105 recognizes the proceed-to-send signal and
responds by sending the keypulse pair of tones followed by the
called number digits, in the conventional manner. Upon completion
of sending the called number, the MF sender 105 disconnects itself
from the outgoing trunk 102.
The destination toll office 20 receives the called number digits
and determines to where the call should be switched. When the
connection to the called party is established, the called telephone
rings.
The telephone set 9 of the calling party is now connected to the
toll office 20 via the speech path of the local office 10, and the
toll office 100 including the AMA trunk 101, the network 103, the
outgoing trunk 102 and the outgoing SF unit 104 which is monitoring
the channel B of the transmission path from the destination office
for an off-hook signal to indicate that the called party has
answered the call. This signal takes the form of the removal of the
2600 hertz signal from channel B. Upon detection of this removal,
the outgoing SF unit 104 changes its DC supervisory signal to the
outgoing trunk 102 which, because it is now disconnected from the
MF sender 105, extends this signal back to the AMA trunk 101. This
supervisory signal is detected by the common controlling means 106
and if it meets the criteria of an off-hook signal, e.g. if it is
at least of 2 seconds duration, the billing equipment 108 is caused
to start timing the call. If the change in supervisory signal is
not of a duration long enough to be recognized as an off-hook
signal, it is considered to be a "hit" or extraneous signal and is
ignored.
All of the above operation is conventional and is common to the
toll telephone network. There are variations in the type of
equipment used to perform the detection and the timing but the
functions are all similar. For example, a commonly used
electromechanical system (number 5 crossbar) does not have a
scanner attached to the AMA trunk but it is equipped with circuits
for timing the duration of supervisory and control signals.
DIALLING OF A FRAUDULENT TOLL CALL
The fraud perpetrator enters the picture when the called party's
telephone starts to ring. At this time, the perpetrator uses his
fraud box 8 to transmit a 2600 hertz tone signal unto the telephone
circuit (speech path) towards the destination office 20. The
incoming SF unit 22 receives this signal and interprets it to be an
on-hook or disconnect signal from the originating office. The SF
unit 22 responds by changing its DC supervisory signal to the
incoming trunk 21 to indicate on-hook and this causes release of
the connection to the called number. However, the connection from
the fraud box user's telephone set 9 to the outgoing SF unit 104
remains established due to the use of the DC supervision on this
part of the connection which is controlled by the calling party's
telephone set 9 being off-hook. At this time, the AMA billing
equipment is still expecting an off-hook signal from the
destination office.
The fraud box user now removes the 2600 hertz tone signal from the
telephone line. The incoming SF unit 22 interprets this removal of
tone as a request for service and causes a second proceed-to-send
signal to be transmitted back to the outgoing SF unit 104, which
changes its DC supervision to the outgoing trunk 102. Because the
sender 105 is not connected thereto, the outgoing trunk 102 extends
the change in supervisory signal which corresponds to the second
proceed-to-send signal to the AMA trunk circuit 101. The presence
of this signal appearing at the AMA trunk circuit 101 is ignored
because the billing equipment is waiting for an answer indication
which is an off-hook signal of at least 2 seconds.
The fraud box user hears switching equipment noise in the telephone
set receiver due to the attachment of the register/sender 24 and
the return of the second proceed-to-send signal. The perpetrator
now uses his fraud box 8 to transmit the MF tones corresponding to
a new called number. The AMA system does not become aware of these
signals because they appear on the speech path of office 100. The
MF tones pass through the telephone circuit to the destination
office register/sender 24 which causes a connection to be
established to the new called number in the conventional
manner.
When the telephone set of the new called number is answered, an
off-hook signal is returned to the AMA trunk circuit 101 where, if
it is maintained for a duration longer than 2 seconds, it is
recognized as an answer indication of the called party by the
billing equipment which records the answer indication and the time
of day. However, the billing equipment associates this answer
indication with the number originally dialled from the use's
telephone set 9. Therefore, the user of telephone set 9 is being
charged at the rate corresponding to his first-dialled call. If
this call was directed at a near toll office whereas his
second-dialled call was directed at a far toll office, the
difference in charges can be very significant.
Several methods have been proposed to intercept these fraudulent
calls. As described above, the commonly used method consists of
detecting the 2600 hertz tone signal which the fraud box user
transmits to cancel his first-dialled call at the destination
office. However, as discussed previously, this method requires very
sophisticated and expensive frequency separation and detection
circuitry because at the time and location that the signal is being
looked for, voice signals having similar frequency components may
be on the speech path if a fraudulent call is not being
dialled.
DETECTION OF FRAUDULENT TOLL CALL
When the fraud box user transmits his 2600 hertz tone signal to
cancel his first-dialled call at the destination office 20, a
second proceed-to-send signal is returned to the outgoing SF unit
104 on channel B of the transmission path. This signal causes a
change in the DC supervisory signal to the AMA trunk 101.
Established criteria of operation dictates that this signal must
have a nominal duration of 200 milliseconds; that is, greater than
75 milliseconds and less than 2 seconds (FIGS. 3 and 4). Therefore,
the detection of this second proceed-to-send signal is achieved by
providing the detection circuitry attached to the AMA trunk 101
with the capability of detecting a DC signal meeting these limits.
In the system embodiment described above, the timing of the
programs controlling the detection of supervisory signals at the
trunk circuit 101 by the common controlling means 106 is altered to
provide the detection and recognition of the second proceed-to-send
signal. These additions to the programs are reflected in the
differences between the sequence flow charts of FIGS. 3 and 4.
These altered programs provide a means of detecting these
fraudulent toll calls. Similarly, in electromechanical systems, the
timing circuits of the detection circuits may be altered to provide
the detection of this fraudulent proceed-to-send signal.
When the fraudulent second proceed-to-send signal is detected at
the originating office, a number of options are opened to the
operating telephone company.
The use of the telephone system may simply be denied the fraud box
user by cancelling his call and entering an identifying code (flag
signal) on the tape 109 of the billing equipment 108. This
procedure may lead to the identification and possible future
prosecution of the fraud perpetrator.
Alternatively, there is provided an MF receiver 110 connectable to
the AMA trunk by means of a switch 111 controlled by the common
controlling means 106. When the fraudulent proceed-to-send signal
is detected, the switch 111 is actuated to connect the MF receiver
110 to the AMA trunk 101 for a maximum time interval of 30 seconds.
Since the MF register/sender 24 at the destination office will time
out 25 seconds after a proceed-to-send signal has been initiated,
the 30 seconds timing of the MF receiver 110 insures that if the
perpetrator does not key his second-called number within that
interval of time, he will have to request service again and the
detection process will be repeated. As the fraud box user transmits
the second-dialled MF signals, they are received at receiver 110
and are then transferred to the billing equipment 108 and the
memory tape 109 together with a coded entry (flag signal) denoting
the existence of a fraudulent call. The call may then be allowed to
proceed. In this case, the fraud box user is identified as is the
destination of his fraudulent call. The user may therefore be
charged correctly for his call.
The circuitry necessary to embody the invention has not been
described to the schematic diagram level because the functions
performed thereby may be achieved using well known circuits. For
example, the MF receiver 110 may be of the type commonly used in
toll offices to receive MF signalling, whereas the switch 11 may be
an electromechanical switch such as relay or a semiconductor switch
using transistors.
Although the invention has been described using the embodiment of a
stored program switching system, it should be realized that it is
equally applicable to electromechanical switching systems. The
timing detection may be achieved simply by connecting the required
timing circuits of any well-known conventional design to the
automatic message accounting trunk circuit of the originating
office and of providing an MF receiver as described above. The
weird logic for controlling the operation of this new combination
of elements may be easily implemented once the content of this
disclosure is known.
The invention provides a reliable method and apparatus for
detecting fraudulent toll telephone calls, and which may be
implemented economically in existing telephone toll offices whether
they are of the stored program electronic switching system type or
of the electromechanical type.
* * * * *